1. Field of the Invention
The subject invention relates to the field of bore hole gauges that are used to measure in-situ the stress and physical properties of solid elastic masses.
2. Description of the Prior Art
In recent years, the primary means of measuring stress changes, absolute stress, or physical properties of a rock mass in-situ is to place some kind of instrument or gauge into a drill hole in the rock mass. The hole boundary then becomes one surface of a rock structure that surrounds the hole. If a gauge is placed in contact with this surface and the surface shape is changed, the gauge can respond to that change. This response is then used to estimate the rock stress or physical properties of the rock mass such as its' Young's modulus or Poisson's ratio.
There are generally two types of gauges. If the gauge changes its' size or shape and applies a pressure or force to the hole surface, the gauge may be called an "active" gauge. If the hole in the rock mass changes its size or shape and applies a pressure or force to the gauge, the gauge may be called a "passive" gauge.
Another way of classifying the "passive" gauges is as "deformation" or "stress" gauges. If the gauge is soft and does not interfere with the displacement of the hole boundary when the rock stress is changed, the gauge is a "displacement" gauge. The rock mass completely controls the resulting hole shape from which the rock stress is calculated from the physical properties of the rock mass obtained in the laboratory. If the drill hole is over-cored to obtain the laboratory sample, the absolute stress can also be calculated in the laboratory.
If the gauge is hard and completely controls the behavior of the hole surface when the rock mass is stressed, the gauge is a "stress" gauge. Since the rock mass contributes little to the resulting shape of the hole boundary, the physical properties of the rock mass are relatively unimportant. In practice, however, the stress gauge is not infinitely rigid and thus deforms, but this deformation is much less than would be the case for the open hole. However, the gauge still controls the behavior, and the physical properties of the rock mass are relatively less important than those of the gauge. This feature of the "stress" gauge is attactive and has resulted in the development of a variety of instruments of this type.
None of the gauges known at this time measure both the physical properties of the Young's modulus and Poisson's ratio, the change in rock stress, and the absolute stress in-situ without making use of laboratory measurements of rock properties.
In this invention, a method is presented which can measure these four quantities in-situ.